Scientific Intelligence. — Meteorology. 188 



constantly serene from the moment when the River Angara, 

 which flows out of Lake Baikal, is covered with ice, to the 

 month of April. In a cold of from 30" to 35° of Reaumur, 

 the sun rises and sets clear, free from the red mist in which its 

 disk appears enveloped to us, when near the horizon, during 

 the winter. iVIoreover, its action is so powerful, in spite of the 

 intense cold, that the roofs of the houses are often seen dripping 

 in a temperature of from 20^ to Q(f helow zero. The latter de- 

 gree of cold is more supportable here than that of 15° with us, 

 seeing that the air is always calm and dry. When we left To- 

 bolzk, on the 12th December, the cold was constantly from 20 

 to 30 to 34°. We are obliged to cover our instruments with 

 thin leather, otherwise, on touching them, a pain was felt hke 

 that from a burn, and a white blister was produced on the 

 skin." 



HYDEOGKAl'HY. 



2. Colour of Water and Ice. — Not only the water, but also the 

 ice of chfferent rivers, has a peculiar colour ; and this appears 

 to depend not on accidental causes, as conjectured by Davy, be- 

 cause, if so, it could not be the same every year. " I have,"" 

 says Ritter von Wurzer, in Karsten"'s Archives, b, xviii. p. 103, 

 " often observed this in the ice of the Rhine, which is always 

 bluish ; while, on the other hand, the ice of the Moselle is al- 

 ways greenish. The ice of the small rivers that pour into the 

 Lower Rhine, for example the Ruhe, &c. is either zchite, or only 

 jjale greenish. More than seventy years ago, Leidenfrost first re- 

 marked this circumstance. This difference of colour is so strik- 

 ing, tliat the boatmen guide themselves by it, as they know by 

 it whether it is Rhine or Moselle ice they have to do with. 

 That decaying vegetable matter is the cause of the green colour 

 is by no means evident, for the clear and transparent ice of the 

 Rhine is sky-blue, the clear and transparent ice of the Moselle 

 is green ; and why is this appearance the same, year after year ? 

 Why is the water of streams in woods in general not green ? 

 Why is the sea-waters green, even in places hundreds of miles 

 from the land ? I am not of opinion that iodine and bromine 

 give to sea-water its colour, for those sea-plants which, by their 

 decomposition, afford these substances, docs not contain them in 



